Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 252357

Area Forecast Discussion
National Weather Service Raleigh NC
655 PM EST Sat Feb 25 2017

A strong cold front currently crossing the area will move offshore
this evening. Colder high pressure will move in from the west
tonight, and linger through Sunday night, before moving offshore
Monday. A warm front will approach from the south late Monday.


As of 330 PM SATURDAY...

Deepening cyclone will lift north into Ontario and Quebec, with
associated strong mid-upper trough over the OH and TN Valleys
becoming negatively tilted as it progress eastward into the Mid-
Atlantic States tonight. Attendant cold front currently approaching
the Triad will advance east through central NC through 00 to 03z.

It will remain breezy ahead of the front, with swly sustained winds
of 15 to 18 kts, gusting to 25 to 30 kts, with similar magnitude
west-northwesterly wind gusts in the wake of the front through 00 to

Dry air and a strong boundary layer mixing is proving difficult to
overcome and will continue to limit convective coverage across the
area through 00z, though there still remains an isolated threat for
a severe thunderstorm across the northern Piedmont and northern
coast plain. Weak to moderate instability(MLCAPE 500-1000 J/Kg) has
developed in response to steep low-level lapse rates from the
unseasonably warm temperatures and mid-level lapse rates of 7.0 to
7.50 C/Km, left behind by the EML that pushed through the area
earlier this morning. Impressive effective unidirectional shear of
50 to 60 kts, coupled with inverted-V sounding profiles and DCape
values of 1000 to 1200 J/Kg from the entrainment of dry air aloft
will make it possible for an isolated severe storm to produce
damaging straight line winds across the northern/northeastern tier,
with even 40 to 50 mph winds possible in the heaviest shower. Hail
up to size of quarters is also possible.

Convection should be exiting the area at or by 00z, with strong post-
frontal dry cold air advection resulting in abrupt clearing and
seasonable overnight lows in the lower 30s NW to upper 30s SE.


As of 315 PM SATURDAY...

Flow aloft will become quasi-zonal flow in the wake of upper trough
exiting the Mid-Atlantic region. High pressure building into the
area from the west will quickly move offshore late Sunday night, but
will maintain east to west surface ridging into Monday. This means
that the cooler-more seasonable air will not stay around very long.
Highs ranging from from mid 50s NW to around 60 SE.

Sheared shortwave energy ejecting eastward across the Lower MS
Valley in the progressive low-amplitude flow will bring an increase
in high clouds late Sunday night/early morning and could temper low
temps Sunday night. Lows in the 30s.


As of 200 PM Saturday...

After the brief return to near normal high temperatures on Sunday,
we will have a progressive warmup back into the 70s through midweek
as high pressure moves offshore and southwest flow ensues. Moisture
will be on the rise, as will cloud coverage and the chance of rain
through the midweek period. Showers are expected as early as Monday
night in the west as a weak upper disturbance lifts northeast in
prevailing southwest flow aloft. It`s hard to find a really
confident feature that might enhance coverage Tuesday night through
Wednesday but we will be in the warm moist airmass with potential
for any passing weak impulse to kick off spotty showers. Will
maintain generally uniform low chance PoPs across the area pending
later model resolution of these impulses. Temps will be rebounding
on Monday into the 60s...with low to mid 70s on Tuesday and mid to
upper 70s on Wednesday.

A cold front driven by a rather strong shortwave moving into the
Ohio valley will provide a focus for a line of convection Wednesday
night in the west...with the convection moving east rapidly and
offshore by Thursday evening. The convection will be east of central
NC by early afternoon. This timing is not ideal to benefit from
maximized diurnal instability, but strong upper diffluence and the
low level convergence with a 50+ knot h85 jet will be sufficient for
inclusion of at least a modest chance of thunderstorms at this
point. Highs Thursday will be hampered by the onset of cold air
advection fairly early in the day, with western areas topping out in
the upper 50s...while the southeast might see some mid 60s.

Dry weather and a cooler airmass will be in place Friday and
Saturday, with highs both days mostly in the upper 50s to lower 60s.


.AVIATION /00Z Sunday through Thursday/...
As of 655 PM Saturday...

VFR conditions are highly likely for the next 24 hours. A cold front
now moving through the area will be east of all central NC terminals
by 04z. Strong and gusty surface winds are shifting with frontal
passage to be from the WNW or NW. Speeds and gusts will diminish by
06z with sustained speeds trending down to under 10 kts. Scattered
showers and storms will impact the northeast forecast area before
03z, however these should largely stay north of RWI. Winds Sun after
14z will be from the WNW or NW at 8-12 kts with a few gusts of 15-20

Looking beyond 00z Mon: High pressure will build over the area from
the west then move east and offshore Sun night, which will bring VFR
conditions through Mon. The next chance for sub-VFR conditions will
be Mon night, lasting through Tue night and perhaps into Wed, as
southwest flow brings in low level moisture and an increased risk
for showers, as well low stratus and fog, especially dusk through
dawn. A cold front passage late Wed night or early Thu will bring a
better chance for showers then. -GIH





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